There has heretofore been developed arrangements for "activating" hydrocarbon fuels prior to combustion in a combustion device by generating radicals of the fuel molecules. This activation reduces ignition delay and allows greater control over the combustion process, and the activation process itself may be employed as an ignition mechanism.
Activation of fuel by formation of radicals may be carried out to a degree in which a sufficiently high concentration of radicals results in negligible ignition delay and the fuel combusts substantially instantaneously when introduced into an oxidizing atmosphere. This combustion of such highly activated fuel is referred to as "hypergolic" combustion, and activation to such levels has heretofore been described as being able to be accomplished in various ways.
In U.S. Pat. No. 4,448,176 assigned to the same assignee as the present application, there is described an activation process in which fuel is heated to very high levels, i.e., to temperatures on the order of 1000.degree. F., to achieve fuel activation resulting in hypergolic combustion when the fuel is introduced into an oxidizing atmosphere.
Various other patents also assigned to the same assignee describe fuel charge activation by electrical discharge, of irradiation by UV and laser beams, heating by compression, as well as catalytic pretreatment of the fuel.
As a particular example, U.S. Pat. No. 4,582,475 describes activation by passing the fuel through an electric field generating a corona, to provide an ignition device by activation of the fuel molecules to an extent sufficient to establish ignition. While suitable as an ignition device, it has been found that the rate of formation of radicals by a corona alone is too low to activate an entire fuel charge for a cyclically operated combustion device such as an internal combustion engine.
It is noted that the persistence of the radicals is short such that injection into an oxidizing atmosphere must occur almost immediately upon activation.
As another example, U.S. Pat. No. 4,672,938 discloses a multiphasic pretreatment of fuel to be burned in an engine, including passing the fuel through an electric discharge, suggested as a corona or an electrical arc.
The localized activation of fuel and air by an arc, as in a spark plug, is inherent in conventional spark ignition. However, there has not heretofore been provided a system for activating more than a minute proportion of a fuel charge by an electrical arc. Such a system would have to expose a substantial proportion of the fuel charge to the arc with an intensity effective to activate such proportion of fuel passed through the system and mix the radicals through the fuel charge to achieve a uniform combustion event. Since the duration of the arc would have to be sustained for a much longer period than in conventional arc ignition systems, electrode erosion is potentially a severe problem, as the metal of the eletrodes would reach elevated levels sufficient to liquify and/or vaporize portions thereof, and to migrate away. This is particularly so for the initially high current levels found in conventional systems when very high voltages are applied, i.e. 25,000 volts or higher needed to jump the spark gap and establish the arc.
The object of the present invention is to provide an arrangement for activating a fuel charge by means of a sustained electrical arc which rapidly activates a substantial proportion of a fuel charge by exposure to the electrical arc while avoiding the electrode erosion problem. This arrangement is thereby adapted to supply activated fuel for hypergolic combustion in an internal combustion engine.